It is a common manufacturing practice to secure nuts directly to sheet metal pieces through a welding process. In the manufacture of motor vehicles today, there are virtually hundreds of applications for such “weld nuts” including various forms of brackets, air bag supports, door parts and many others.
In general the weld nut is resistance welded to a metallic component by the weld gun. The weld nut is loaded onto a lower electrode. An upper electrode is moved into contact with the weld nut. A very high current is applied to the electrodes and the weld nut is welded to the metallic component.
A variety of welding assemblies have been utilized for the production of weld nuts. One of the most common assemblies employs upper and lower welding units and a retractable steel locating pin. See, for example, U.S. Pat. No. 2,731,535 issued to Grey. As discussed by Grey, in operation, a sheet metal piece with a preformed aperture is loaded on top of the lower welding unit such that the aperture is aligned directly over the locating pin recessed within the lower welding unit. The locating pin is then extended through the aperture of the sheet metal piece to capture a nut fed from a weld nut feeder positioned above and to one side of the locating pin. The nut is then centered about the locating pin over the aperture by the force of gravity. The upper welding unit then descends over the nut and a voltage differential is applied between the upper and lower welding units to fuse the nut to the sheet metal piece. Finally, the upper welding unit is withdrawn, the locating pin is retracted into the lower welding unit, and the sheet metal piece is removed from the welding assembly.
Significantly, this conventional type of welding assembly is known by those skilled in the art to suffer from a problem with respect to weld nut orientation. Occasionally when the weld nut is released from the feeder onto the component to which it is to be attached, the weld nut drops face up such that the weld projections face away from the component to which the weld nut is to be welded, resulting in the wrong orientation of the weld nut. In such instance the weld nut cannot be properly attached to the component.
In response to the occasional problem of incorrect orientation, a fiber optic sensing system has been developed which measures the distance traveled by the nut weld pin. This distance is compared with pre-programmed set point values. If the distance measured agrees with the pre-programmed set point values, then a weld occurs. If the distance measured disagrees with the pre-programmed set of values, then a weld will not occur.
While representing an improvement in the state of the art regarding weld nut orientation, the known fiber optic systems suffer from poor quality and are costly to purchase and to maintain.
As in so many areas of component assembly technology, there is room in the art of weld nut orienting detection systems which will help to avoid some of the limitations of known designs.